1. Field of the Invention
This invention relates to water wells, and more particularly to an improved method of removing deposited material from a well and the surrounding aquifer. This method generally comprises initially properly evaluating problems associated with a particular well and then utilizing the controlled and telemetry-monitored injection into the well of energy derived from phase changes in solid, gaseous, and liquid carbon dioxide (CO2) to remove such deposited material.
2. Description of the Prior Art
The prior art reveals techniques for stimulating the flow of water in a dry well or one providing insufficient water. For example, in U.S. Pat. No. 5,394,942 issued to Catania, et al., the disclosures of which are herein incorporated by reference, pressure in a dry or inefficient well is regulated to a desired level through use of a sealing cap, and nontoxic gaseous and liquid carbon dioxide (CO2) is introduced into the well. The pressure and flow of gaseous and or liquid are regulated to such a level, between about 0 and 70 psi pressure, that the liquid CO2, upon entering the sealed well, rapidly solidifies within the well. This liquid CO2 can be added until the well is filled with solid CO2; the solid sealed CO2-filled well is then allowed to sit, and the solid CO2 gradually sublimes. Because of the temperature differential between the well formation and the solid CO2, the solid CO2 sublimates releasing gaseous CO2 into the formation; consequently carbonic acid (H2CO3) is produced upon contact of the CO2 with water in the formation. The presence of the H2CO3 in the well aids in the removal of bacteria from surfaces in the formation, especially iron-related bacteria, such that a bactericidal effect can be achieved. After the solid CO2 sublimation is completed, any residual pressure in the well is released, and the well is unsealed. Additionally, because of the freezing within the well and well formation, encrustation in the well from such material as drilling mud, natural clay and silt, and other physical blocking agents and/or mineral scaling in the well formation and in the well screens is removed. If desired, the process may be repeated until the flow of water into the well is sufficient.
However, every well that is to be treated with such a process is slightly different than any other well to be treated. Prior to treating a dry or inefficient well, it is therefore desirable to evaluate the aquifer and the type of problem in the well. This evaluation shall aid the determination of the most effective method of delivering the requisite energies of agitation, dissolution, and detachment delivered during the phase changes of CO2 to allow the effective cleaning of deposits from the surfaces of a well and the surrounding aquifer. For example, the amount of injection of energy during the process disclosed in U.S. Pat. No. 5,394,942 can vary depending upon well design, well problems, well construction, and site considerations.
Additionally, the liquid CO2 is most often introduced into a well in short pulses of liquid while still feeding gaseous CO2. These short pulses are for the purpose of determining how a water well will respond to the injection of the additional energy. It is very important to observe the various pressures during the stages of liquid CO2 injection, because the pressures of injection can range from 0 to 300 psi depending on the individual type of well. It is therefore desirable to provide a method of injection of CO2 into a well to clean out deposited material wherein real-time monitoring of the pressures and temperature inside the well takes place. This monitoring would provide the information necessary to determine the required injection rates of gaseous and liquid CO2 in order to manipulate the phases of CO2 and phase changes in the well, and therefore allow better control of the energy delivery into the well.
Finally, due to the physical properties of CO2 and the conditions inside a well when CO2 is injected, not all the desired phase changes can be achieved with just the injection of gaseous and liquid CO2. In deep wells or wells that have a hydrostatic pressure greater than 75 psi, desired phase changes are not always achieved. Inside a well and under hydrostatic pressures greater than 75 psi, a well is very similar to a pressure vessel, with a phase change taking place from pressure dissipating into the surrounding aquifer and with temperature changes as calories are transferred to and from the water and surrounding formation. When the pressure in the well is greater than 75 psi and the hydrostatic pressure is greater than 75 psi, liquid CO2 would penetrate into the surrounding formation and then convert to a gas without going to a solid. This would be a more rapid phase change than is sometimes desired. Consequently, it is desirable to have a method of temperature and pressure manipulation which will allow for more efficient and useful phase changes in the CO2 in the well.